The present invention relates to a metallurgical apparatus and a method of circulating molten metal within a metallurgical apparatus.
In one embodiment, the invention relates to a furnace for melting metals including, but not limited to, non-ferrous metals such as aluminium, magnesium and zinc. Such furnaces generally include a circulator device for circulating the melt within the furnace to ensure even heating and distribution of alloys. Various circulator devices are known, including mechanical pump, electromagnetic pumps, agitating and stirring devices.
JP 10146650A describes a furnace with an electromagnetic inductor stirring device comprising a disc-shaped permanent magnet located below the floor of the furnace. The magnet can be rotated and the resulting rotating magnetic field causes rotation of the melt in the furnace by electromagnetic induction. The disclosure of JP10146650A is herein incorporated by reference.
EP 1674814A describes an agitator for agitating a melt, which has a plurality of permanent magnets mounted on a motor-driven rotor. Rotation of the rotor creates a rotating magnetic field, which can be used to pump melt through a passageway that extends between inlet and outlet openings in a wall of the furnace. This causes circulation of the melt in the furnace. The disclosure of EP1674814A is herein incorporated by reference.
US 2011/0248432A1 describes an electromagnetic pump that has a plurality of permanent magnets mounted on a motor-driven rotor. A spiral passageway extends through a housing that surrounds the rotor and melt can be pumped through this passageway by the rotating magnetic field created by the rotating magnets. The disclosure of US2011/0248432A1 is herein incorporated by reference.
Hertwich Engineering of Braunau Austria supply a range of electromagnetic pumps and stirrers for circulating and mixing molten metal. These devices include side channel pumps and stirrers, which use an electromagnetic pump to pump melt through a side channel formed in the wall of a furnace, and a tube pump that uses an electromagnetic pump to pump melt through a tube, for example from one chamber of a furnace to another.
WO2014/202966A1 describes a metallurgical vessel for holding and circulating a body of liquid metal. The vessel has a peripheral wall and a circulating apparatus comprising a launder than provides an open-topped flow channel. The disclosure of WO2014/202966A1 is herein incorporated by reference.
The above-mentioned circulator devices all include one or more disadvantages. The external electromagnetic stirring device described in JP 10146650A is expensive to implement and the magnetic field produced by the permanent magnets penetrates the metal to only a fixed shallow depth which does not drive circulation of the metal efficiently. The magnetic rotors described US 2011/0248432A1 and EP 1674814 only act on a limited amount of metal in the melt passageways, producing only a relatively weak flow. The melt passageway also has to be designed so the metal remains in close proximity to the magnetic rotor for as long as possible, which restricts the shape of the passageway to a relatively narrow U shape and so dictates the flow direction of metal as it leaves the passageway. The melt passageways of the systems described US 2011/0248432A1 and EP 1674814, as well as the circulator devices supplied by Hertwich Engineering, cannot easily be cleaned and can become blocked by dross and other materials. Also, where the external passageways are provided, these cannot always be preheated effectively, giving rise to a risk that they could become damaged by thermal shock upon contact with the molten metal, or they could cause the metal to freeze thereby blocking the passageway.